2)At the current speed at which battery technology is advancing, in 10 years we may be able to run an electric motor on batteries alone for 4 hours or so.
...

3)If we advance motor tech at the same rate then we will have smaller and more efficient propulsion.

1) Maybe, but I doubt it.

2) Batterystorage capacity isn't advancing all that quickly. It is advancing at about 4% a year. But even assuming this continues uninterrupted until it hits the absolute maximum physics allows, batteries will only be 4 times more energy dense than they are now. That is to say that batteries right now are storing about 25% of the maximum possible energy they ever will be able to. This is due to limits on the electron density of atoms, and cannot be broken.

Given that diesel has a usable energy density of about 50 times that of the best batteries there is really no practical point at which batteries can compete. We need something else.

3) The best EP motors are currently running at a peak efficency of about 98%. That is for every 1kw put into the motors they generate 980kw of shaft power. There simply is no possible gain to be made here. The cheapest least efficent EP motors operate at >80% efficency, so there is a little gain, but the technology is already on the shelf, it isn't even that much more expensive.

Sadly the gain you hope for are not really there with current technology, or even possible future technology without a paradigm shift.

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Greg

- If animals weren't meant to be eaten then they wouldn't be made of food.

2) Battery storage capacity isn't advancing all that quickly. It is advancing at about 4% a year. But even assuming this continues uninterrupted until it hits the absolute maximum physics allows, batteries will only be 4 times more energy dense than they are now. That is to say that batteries right now are storing about 25% of the maximum possible energy they ever will be able to. This is due to limits on the electron density of atoms, and cannot be broken.

Given that diesel has a usable energy density of about 50 times that of the best batteries there is really no practical point at which batteries can compete. We need something else.

3) The best EP motors are currently running at a peak efficency of about 98%. That is for every 1kw put into the motors they generate 980kw of shaft power. There simply is no possible gain to be made here. The cheapest least efficent EP motors operate at >80% efficency, so there is a little gain, but the technology is already on the shelf, it isn't even that much more expensive.

Sadly the gain you hope for are not really there with current technology, or even possible future technology without a paradigm shift.

The one factor omitted from your otherwise good assessment is the ability to refuel along the way with solar. We might see a doubling of solar panel efficiency in the next few years (an Aussie lab is already testing cells that have "layers" that absorb different frequencies and have reached 40%). We might get to four or five hours a day of 7 knot cruising, and that's all lots of people do.

The one factor omitted from your otherwise good assessment is the ability to refuel along the way with solar. We might see a doubling of solar panel efficiency in the next few years (an Aussie lab is already testing cells that have "layers" that absorb different frequencies and have reached 40%). We might get to four or five hours a day of 7 knot cruising, and that's all lots of people do.

If you cover a 40' cat with the best solar panels available commercially now (about 20% efficent) that works out to be about 40kwh a day of production. If you double it that gives you about 80kwh a day. A 40' cat operating at 7kn is going to need something like 20kw/hr. So your estimate that if we can somehow double the collection efficiency of pv panels you could motor for 4 hours is pretty spot on.

But it still isn't very practical.

First even assuming you get to 40% efficent panels I wouldn't accept a 28nm range. It just isn't far enough.

Second that works out to a little better than 1nm/hour on average. Even in dead light air a heavily loaded cruising cat should be faster than that. So it will still be far faster to sacrafice panel space for sails.

Third, the battery technology doesn't exist to store much of that generated power when you aren't moving. So you can't even fill the tanks while at anchor. Maybe you can store a few hours worth of run time with the best batteries theoretically possible, but it won't get much better.

Right now the most promising solution I see on the horizon to get rid of diesels would be the ability to crack ocean water into hydrogen and oxygen. Compress the gas for storage, then use a fuel cell to power the boat while underway. But I am not sure what round trip efficentcy would be, or how far out this technology really is.

For the forseable future this all works out to diesel power. Either diesel powered prime movers, or diesel powered generators.

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Greg

- If animals weren't meant to be eaten then they wouldn't be made of food.

Sadly the gain you hope for are not really there with current technology, or even possible future technology without a paradigm shift.

A paradigm shift could be making hulls, mast or even sails out of carbon nano tube batteries turning the structure of the boat into battery storage.

They are working out carbon nano batteries with energy densities equivalent to Li-Ion and it has great mechanical properties. Also since carbon is easily found and isolated no horrid lithium mining and easier production.

Hate to be the cynic - but the energy requirement needed to perform electrolysis and compression are pretty easily defined and there's no way boats will be producing compressed hydrogen for fuel cells or even hydrogen ICE. Energy demands are just too high.

You'll be better off with the best panels and batteries available and use a very efficient and small generator to power batteries and an electric motor.

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We are sailors, constantly moving forward while looking back. We travel alone, together and as one - to satisfy our curiosity, and ward off our fear of what should happen if we don't.

The one factor omitted from your otherwise good assessment is the ability to refuel along the way with solar. We might see a doubling of solar panel efficiency in the next few years (an Aussie lab is already testing cells that have "layers" that absorb different frequencies and have reached 40%). We might get to four or five hours a day of 7 knot cruising, and that's all lots of people do.

Don't forget as efficient as electric motors are at using electricity, converting that energy to chemical (aka: battery) and then back wastes lot, meaning the overall system is very inefficient.

But we are no where close to making cost effective solar systems that come anywhere close to producing enough power to have any significant cruising range.

I guess these guys were lying too: "I call it putting the motors in step," says Scott. "If you set it just right, you get Scott. "If you set it just night, you get a zero net use of electricity. And you also get an additional one-half to one knot of boat speed. There's a net speed increase,"

Let's for a minute assume they can put the motor's "in step".

When would this be useful:
- When fully under motor or motor sailing, the wave action is typically fairly light, so there is little to nothing to gain.
- When the wave action is strong and the system could "theoretically" do something, you have enough power from wind alone to chug along at hull speed.

Yeah, there might be the rare day when you have a storm just past and the waves haven't settled yet but I can't see it being useful very often.

Of course, I'm not buying the "in step" theory in the first place but why bother when it's only useful in rare situations.

Only a couple of these are actually real. One cost 26 million and the other one is unmanned, travels at 1.5 km an hour and appears to be stuck in the Atlantic. It certainly won't reach Portugal in October if the last 4 months are anything to go by.

It's not like a car in stop-&-go traffic where a hybrid can create impressive increases in MPG by storing energy during idle and braking and using that energy during acceleration. Cruising boats usually get up to speed and stay there for hours (or sailing purists only run them for 10-15min to get in and out of port, so there is no significant savings to be had). Assuming the conventional diesel is properly sized, that means it's running at a very efficient rpm/torque range when at cruise sped. With the additional energy conversions with a hybrid you are at best going to come close to what a conventional drive can do.

If you are thinking to use the generator for house loads, it will typically be massively oversized and inefficient compared to a properly sized dedicated generator. (if you size it for house loads, it will be too small for propulsion loads)

Hybrid makes no sense on a boat.

Now if you are a purist sailor, just want something to get in and out of port and don't care about resale value, a pure electric boat is viable.

All things being equal a hybrid cat may make sense. Electric motors weigh a lot less than iron diesels so trim can be optimized. One gen set can run both props and provide house power. The location is not critical. Only one diesel is required which reduces maintenance. Modern diesels are not as bad as some think in relation to running with variable loads.

So while certainly not maintenance free they aught to be "less maintenance" if designed and installed correctly.

there are a ton of valid points being made for and against electric, but i truly believe there is a simple rule to if electric is for you (or at least a precursor to the argument) when a gallon per mile is considered good, you're consuming a TON of energy that current electric technology won't fill. a sail/electric combo does well, but if you plan a lot of electric power cruising, get used to the view at the marina. my intended use happens to be very limited travel, so i may take the dive into an electric conversion on a big power boat someday. however, i'd be dumping a ton more money in quadrupling the battery storage, and i won't have any unrealistic expectations in replacing 1,000 gallons of on-board diesel for electric.

It's important to understand the realistic cruising possibilities of EP. The idea of needing 1,000 gallons of fuel to drive the EP for a big motor cruiser via DC genset is very sobering.

Since we are looking at a multihull forum, I think it's right to realise that multihulls are probably the best application for cruising with EP. Why? Because the useable range and hull speed at CRUISING speeds are entirely achieveable with multihulls that have suitable displacement and hull form.

For continuous motoring, the "7 at 7" is an achieveable goal, that is, 7 knots of cruising speed using 7 kW of power, in slight seas for a 45' cruising cat with reasonable hull form and displacement. Big fat hulls on heavy condomarans will get less performance, and slim 'n slippery hulls with a light boat can get more.

What you find is that there is a sweet spot for cruising hull speed vs kW consumed, and you can run the DC genset to generate that kW battery charging so you do not eat into your propulsion battery reserves. So you run on a nett zero battery use.

OceanVolt do that analysis for you, and they err on the conservative side. The speed vs kW used curve shows that you can get more speed, but you use MUCH more power to get that extra knot or two, compared to the sweet spot.

We will be using a 10kW DC genset on our 50' cat to give us a bit more grunt for adverse conditions when/if necessary such as tidal sets or coral pass current. BUT, we plan on sailing the boat, because it sails so well. When we are becalmed, "7 at 7" will do us just fine using 3 liters/hour on the DC genset running at maximum efficiency. We are deciding now on how much diesel tankage we'll need, but one thing is for sure, it sure ain't 1,000 gallons!!!